In recent years, attention has been given to display devices in which a touch detection device referred to as a so-called touch panel is provided on a display device such as a liquid crystal display device, or a touch panel and a display device are integrated as a single body, and the display device is made to display various button images to enable information to be input without ordinary real buttons. Such display devices having a touch detection function do not need input devices such as a keyboard, a mouse and a keypad, and thus tend to be broadly used as display devices of computers, portable information terminals such as cell phones, etc.
As such a touch panel, a capacitive touch panel is known in which a plurality of electrodes each formed to extend in a single direction are intersected to each other. In this touch panel, the electrodes are connected to a control circuit, and when supplied with an excitation current from the control circuit, they detect proximity of an external object.
As a display device having a touch detection function, a so-called in-cell touch panel is proposed in addition to a so-called on-cell touch panel in which a touch panel is provided on a display surface of a display device. In the in-cell display device, a common electrode for display, which is originally provided in the display device, is also used as one of a pair of electrodes for a touch sensor, and the other of the pair of electrodes (a touch detection electrode) is provided to intersect the common electrode.
A display device having a touch detection function is disclosed (in Jpn. Pat. Appln. KOKAI Publication No. 2012-48295) in which drive electrodes for touch sensor are sequentially selected in a time sharing manner such that a predetermined number of drive electrodes for touch sensor are selected at a time; a touch detection drive signal is supplied to selected drive electrodes; and a scanning drive is performed at a scanning pitch which is smaller than the total width of the selected drive electrodes.
It should be noted that in a drive method disclosed in the above patent publication, it is necessary to synchronize a display operation and a touch drive operation with each other in order that they be performed in a time sharing manner in a single frame period. Thus, in the above touch detection device, a touch driver (TPIC) which controls the touch drive operation and a display driver (DDI) which controls the display operation execute a touch drive control in cooperation with each other.
Also, it should be noted that the touch driver TPIC and the display driver DDI are configured to operate in synchronism with clocks generated by standard frequency generators provided in the touch driver (TPIC) and the display driver (DDI), respectively. That is, clocks for the operations of the touch driver (TPIC) and the display driver (DDI) are different from each other in master clock. Therefore, it is necessary that the touch driver (TPIC) and the display driver (DDI) are designed in consideration of the case where the difference between the clocks for the touch driver (TPIC) and the display driver (DDI) is the maximum (the worst case).